Field effect transistors based on organic semiconductors are of interest for electronic applications that require extremely low production costs, flexible, or unbreakable substrates, or fabrication of transistors and integrated circuits over large areas. For example, organic field transistors are used as pixel control elements in active matrix screens. Such screens are usually produced with field effect transistors based on amorphous or polycrystalline silicon layers. Temperatures of more than 250° C. are usually necessary for fabricating high-quality transistors based on amorphous or polycrystalline silicon layers require the use of rigid unbreakable glass or quartz substrates. Due to the relatively low temperatures at which transistors based on organic semiconductors are fabricated, e.g., usually less than 200° C., organic transistors permit production of active matrix screens using inexpensive, flexible, transparent, unbreakable polymer films with considerable advantages over glass or quartz substrates.
Another application for organic field effect transistors is fabrication of very inexpensive integrated circuits used, for example, for active labeling and identification of merchandise and goods. These transponders are usually produced using integrated circuits based on monocrystalline silicon, which leads to considerable costs in the construction and connection technology. Producing transponders based on organic transistors leads to enormous cost reductions and assists in increasing transponder technology en route to a worldwide breakthrough.
The fabrication of thin-film transistors usually requires a large number of steps in which the different layers of the transistor are deposited. In a first step, the gate electrode is deposited on a substrate, then the gate dielectric is deposited on the gate electrode, and the source and drain contacts are deposited and then patterned. Finally, the semiconductor is deposited between the source and drain electrodes on the gate dielectric.
Efforts to simplify the fabrication process for field effect transistors and to fabricate the field effect transistors with smaller dimensions have been made. Fabrication of organic field effect transistors requires a targeted patterning of the gate dielectric layer since the targeted access necessary for operation of the transistors to the electrodes or contacts in the metallization plane or the metallization planes below an insulating layer of a substrate (i.e., the substrate in which the transistors are formed) are produced by through-plating (also referred to as contact hole or “via”) in the insulating layer. An access to the metallization planes situated below the insulating layer is necessary, if the input of one transistor is to be linked to the output of another transistor, as is necessary in many cases in almost every integrated circuit.
In recent years, a plurality of microelectronics elements have been described which have a size of a few nanometers and require no lithographic methods or fewer lithographic steps to be fabricated. These elements are nanoelements fabricated by nanotechnology. The elements have a self-assembled molecular layer (self-assembled monolayer).
When using conventional gate dielectrics, such as silicon oxide and aluminum oxide, for example, the contact holes are opened after deposition of the initially closed dielectric layer. For patterning the gate dielectric, a photoresist is applied, exposed, and developed. Then, the gate dielectric is removed by an etching process in regions of the envisaged contact holes. The photoresist protects the regions that are not to be etched. Finally, the photoresist mask is again removed.
This method is unsuitable for patterning molecular self-assembled monolayers. Photoresists are generally developed in a basic solution, which leads to destruction of the monolayer. Coating monolayers with resist is difficult due to strongly hydrophobic nature of many self-assembled monolayers.